The present invention relates to the apparatus and methods used to form apertured pads. More specifically, the present invention relates to apparatus and methods used to form absorbent apertured pads which may be used in such products as disposable diapers, training pants, incontinence garments, catamenial products and other absorbent articles.
Conventional absorbent pads often consist primarily of a cellulosic fluff or other fibrous material. Such absorbent pads may be used in the manufacture of products subject to surge loadings. The expected surge loadings may exceed the rapid intake capability of conventional absorbent pads. Apertures placed in the pads, however, can enhance the rapid intake capability of the pad. Such apertures may consist of empty voids or be filled with a material having different properties than the remainder of the pad.
Such apertures may be employed for purposes other than enhancing the rapid intake capability of the pad. For example, when the apertured pad is used in a disposable diaper, the apertures may provide additional void space for storing and receiving solid wastes or to provide space for the expansion of superabsorbent materials.
The conventional manufacture of apertured pads involves air laying a fluff pad on a forming drum. The pad is subsequently apertured in a separate cutting, calendering or similar procedure. U.S. Pat. No. 5,242,435 discloses, inter alia, the calendering and perfembossing of a cellulosic pulp fluff sheet. U.S. Pat. No. 5,785,697 discloses a different method of forming an apertured pad which involves, inter alia, the use of raised portions on a forming surface employed to form an absorbent composite web.
The present inventors have recognized difficulties and problems inherent in the prior art and in response thereto have developed an improved apparatus and method for forming an apertured pad.
In one aspect, the present invention provides an apparatus for manufacturing a pad wherein the apparatus comprises, i.e., includes but is not limited to, a rotatable forming screen which has a generally cylindrical surface and at least one outwardly projecting nob. The nob is located on the screen in a position whereby the nob is circumscribed by the forming screen. The forming screen is rotatable at a rate which defines a first tangential velocity of the screen. A material source is positioned adjacent the forming screen whereby a material layer may be air layered on the forming screen and the nob may be circumscribed by the material layer. The deposited material layer has a first surface in contact with the forming screen and an opposite second surface. A moveable transfer surface is engageable with the second surface of the material layer. The transfer surface is moveable in a direction which substantially corresponds to the movement of the material layer and at a second velocity which is at least as great as the first tangential velocity of the forming screen. The apparatus also includes a means for attracting the material layer to the transfer surface which may, in some embodiments, be a vacuum source disposed in operative communication with the transfer surface. The nob located on the forming screen includes a thrust surface disposed on a trailing edge of the nob. The thrust surface imparts a compressive force on the material layer at the point where the material layer is engageable with the transfer surface and as the forming screen and the transfer surface move at their respective first and second velocities. The compressive force exerted by the thrust surface of the nob includes a component vector which is directed towards the transfer surface.
In some embodiments of the apparatus, the velocity of the transfer surface may be 101, 102, 103, or a greater percentage of the tangential velocity of the forming screen at the transfer location.
In other embodiments of the apparatus, the transfer surface may be either a flat surface or a substantially cylindrical surface. In those embodiments wherein the transfer surface is a substantially cylindrical surface, the forming screen can have a radius which is less than, approximately equivalent to, or larger than the radius which defines the transfer surface. When the forming screen has a larger radius, the forming screen radius may be greater than twice or three times the magnitude of the transfer surface radius.
The nob disposed on the forming screen can have many different shapes. The nob may have sidewalls which incline inwardly by about 5xc2x0 to form an angle of approximately 85xc2x0 with the forming screen. Such nobs may have a shape which defines a frustum.
The apparatus may also include a plurality of nobs located on the forming screen. The nobs may also be reattachable to the screen as, for example, by using threaded fasteners to secure the nobs to the forming screen. The use of reattachable nobs allows the nobs on the forming screen to be exchanged in a relatively convenient manner.
The present invention also provides a method of forming an apertured pad. One such method includes providing a forming screen with at least one outwardly projecting nob and rotating the forming screen whereby the screen has a first tangential velocity. A pad is formed on the forming screen whereby the pad completely encircles the nob. The pad has a first surface in contact with the forming screen and an opposite second surface. A moving transfer surface is provided adjacent the second surface of the pad and is moved in a direction which substantially corresponds to the movement of the pad and at a velocity which is at least as great as the tangential velocity of the forming screen. The transfer surface is engaged with the second surface of the pad and the pad is transferred to the transfer surface. During the transfer of the pad, a trailing edge of the nob exerts a compressive force on the pad wherein the compressive force includes a component vector which is directed towards the transfer surface.
In some embodiments of the method, the velocity of the transfer surface may be 101, 102, 103, or greater percentage of the tangential velocity of the forming screen at the transfer location.
In other embodiments of the method, the transfer surface may be either a flat surface or a substantially cylindrical surface. In those embodiments wherein the transfer surface is a substantially cylindrical surface, the forming screen may have a radius which less than, substantially equivalent to, or greater than the transfer surface radius. When the forming screen has a larger radius, the forming screen radius may be greater than twice or three times the magnitude of the transfer surface radius.
A variety of differently shaped nobs may be used with the methods of the present invention. The nobs may have sidewalls which incline inwardly by about 5xc2x0 to form an angle of approximately 85xc2x0 with the forming screen. Such nobs may also have a shape which defines a frustum. A plurality of nobs may be used on the forming screen. The nobs may also be reattachable to the screen as, for example, by using threaded fasteners to secure the nobs to the forming screen. The use of reattachable nobs allows one or more of the nobs present on the forming screen to be exchanged for a different nob in a relatively convenient manner.
The apparatus and method of the present invention provide numerous advantages. The configuration and relative motion of the forming screen and transfer surface of the apparatus and method allow the trailing edge of the nob to exert a compressive force on the fluff pad which includes a component vector directed towards the transfer surface. That portion of the compressive force which is directed towards the transfer surface assists in the transfer of the pad to the transfer surface.
Furthermore, by having the trailing edge of the nob exert a compressive force on the pad, the leading edge of the nob will not exert a compressive force on the pad. If the leading edge of the nob were to exert a compressive force on the pad, there would be a significant possibility of the nob damaging or removing the pad material adjacent the leading edge of the nob. In contrast, the apparatus and methods of the present invention create an aperture with a relatively cleanly defined perimeter.
The apparatus and methods of the present invention also provide for the efficient manufacture of apertured pads. No post-formation cutting or calendering operation is required to form apertures in the pads of the present invention. Furthermore, the elimination of the post-formation cutting or calendering operation also eliminates the scrap and additional handling associated with such a post-formation aperturing process.
Another advantage of the present invention is that it may be implemented using reattachable nobs. When reattachable nobs are used, they may be easily exchanged for differently configured nobs. This ability allows the aperture size and geometry to be easily adjusted to optimize the performance of the pad.